Various materials have been proposed and utilized as insulating barriers, including thermoformable composites and laminates. In certain applications, such as vehicle headliners, the insulating barrier must be able to withstand temperatures up to about 200.degree. F. for several hours without sagging, absorb sound at a wide range of frequencies and provide an attractive wear and scuff resistant finish surface. As will be understood, these requirements are difficult to achieve and have not been achieved by the prior art.
A typical thermoformable laminate used for automotive headliners is disclosed in U.S. Pat. No. 4,695,501, the disclosure of which is incorporated herein by reference. As shown in FIGS. 3 and 4 of such patent, the laminate includes polymeric foam laminae which are adhesively bonded and enclosed by "fabric" laminae, which are fiber mats impregnated with a thermoformable polymeric resin. In the commercial embodiment, the fiber of the mats has a fineness of about six denier and the foam is a closed cell styrene-maleic anhydride structural foam. The resultant laminate is subject to sagging at elevated temperatures because the nonwoven mat is bonded directly to the automotive roof. Finally, this laminate has poor sound attenuations particularly at lower frequencies. Thus, the automotive companies have required substantial improvements in structural integrity and sound attenuation.
Automotive headliners have evolved from a fabric layer on fiberboard to composite thermoformable laminates specifically designed or adapted to the requirements of the automotive original equipment manufacturer and the particular vehicle design. The technology of sound attenuation barriers, such as office partitions, has also evolved from a fabric covered foam to improved designs specifically adapted to provide an attractive self-supporting structures including composite laminates. The need, however, remains for improved thermal and sound barriers which are dimensionally stable and which absorb sound in a broader range of frequencies. The use of a porous foam or fiber mat substrate, as disclosed in several prior art patents, results in sound attenuations at the higher frequencies. Alternatively, the barrier can be designed to absorb sound in the low to mid range of frequencies. The need, however, remains for an improved sound attenuation barrier which is structurally stable, particularly at elevated temperatures, and which is capable of absorbing sound in a broad range of frequencies.